1. Field of the Invention
This invention relate to valve actuating devices for internal combustion engines in general, and more particularly to a valve actuating device including a hydraulic valve lifter disposed in a rocker arm of a valve train of the internal combustion engines.
2. Description of the Prior Art
In the valve train of the internal combustion engines, predetermined valve clearances are generally provided in order to compensate for thermal expansion of various parts in the valve train. However, if the valve clearance is not properly maintained at a predetermined valve, undesirable noises are generated during the engine operation, and power losses are caused by blowing of raw gases. Hydraulic valve lifters have been used in the valve train so as to automatically take up the valve clearance in the valve train to thereby prevent the undesirable noises and the power losses.
An example of this type hydraulic valve lifter is disclosed in the Japanese published patent application No. 53-16112, wherein a hydraulic valve lifter is slidably disposed in the rocker arm which receives at one end a load from a cam and actuates at the other end thereof a valve stem. The valve lifter includes a plunger member which engages at one end with the valve stem or the cam and defines at the other end thereof a pressure chamber, a reservoir chamber formed in the rocker arm, and a check valve which allows the flow of a hydraulic fluid, such as lubricating oil of the engine, from the reservoir chamber to the pressure chamber. The reservoir chamber receives the oil from a source by means of both an oil supply passage formed in the rocker arm and an oil supply passage formed in a hollow portion of the rocker shaft. In the above-mentioned conventional valve lifter, however, when the number of the engine rotation increases or decreases suddenly, in particular at the start time of the engine, bubbles may be generated in the engine oil supplied to the reservoir chamber through both oil supply passages. If the bubbles are in excess in an upper portion of the reservoir chamber, the bubbles will enter into the pressure chamber from the reservoir chamber, whereby the stiffness of the valve lifter can be removed and striking noises can be generated.